RE: [PATCH 1/1] x86: Hyper-V: Mark the Hyper-V clocksource as being high resolution

[KY Srinivasan]

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@xxxxxxxxxxxxx]
> Sent: Saturday, July 4, 2015 1:11 AM
> To: KY Srinivasan
> Cc: x86@xxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx;
> apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; Vivek Yadav
> Subject: Re: [PATCH 1/1] x86: Hyper-V: Mark the Hyper-V clocksource as
> being high resolution
> 
> On Fri, 3 Jul 2015, K. Y. Srinivasan wrote:
> > From: Vivek yadav <vyadav@xxxxxxxxxxxxx>
> >
> > By design, alternative clock sources listed are based on the resolution of
> > current clock source. Once you set a  high resolution clock,
> > only high resolution sources are returned.
> > Mark Hyper-V clock source as a high resolution clock source.
> >
> > Signed-off-by: Vivek yadav <vyadav@xxxxxxxxxxxxx>
> > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/mshyperv.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c
> b/arch/x86/kernel/cpu/mshyperv.c
> > index 9b5d7b5..0e507a0 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -151,7 +151,8 @@ static struct clocksource hyperv_cs = {
> >  	.rating		= 400, /* use this when running on Hyperv*/
> >  	.read		= read_hv_clock,
> >  	.mask		= CLOCKSOURCE_MASK(64),
> > -	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
> > +	.flags		= CLOCK_SOURCE_IS_CONTINUOUS |
> > +			  CLOCK_SOURCE_VALID_FOR_HRES,
> 
> No, this is wrong. The CLOCK_SOURCE_VALID_FOR_HRES flag is managed by
> the core code and set when a clocksource fulfils the criteria.
> 
> The changelog above is not explaining what problem you are trying to
> solve.
> 

I think the problem Vivek was trying to solve is that after the Hyper-V clocxk was
installed, if the user switched to another clocksource,  say tsc, the hyper-V clock source would not
listed. I will investigate this further and let you know. Thanks for the feedback.

Regards,

K. Y 
> 
> 	tglx
> 

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